OBD-II code family
EVAP System, Leak and Purge Flow Faults (6 codes)
6 related fault descriptions. Use each full code and the exact vehicle service information to identify its circuit, monitored condition, and required tests.
Codes in this family
This is the complete published member list for this guide. Each code retains its own page; shared diagnostic context does not mean that every member has the same test or repair.
- P0440Evaporative Emission Control System Malfunction
- P0441EVAP System Incorrect Purge Flow
- P0442Evaporative Emission System — Small Leak Detected
- P0455Evaporative Emission System — Large Leak Detected
- P0456EVAP System Very Small Leak Detected
- P0457Evaporative Emission System Leak Detected (Fuel Cap Loose/Off)
What these codes mean
P0440 describes a general evaporative-emission system fault; P0441 concerns incorrect purge flow. P0442, P0455 and P0456 identify small, large and very-small leak-monitor categories, while P0457 adds the fuel-cap-related condition. General system, flow and sealing results should be kept distinct when choosing the next test.
The monitor reports a result rather than physically measuring a hole or inspecting a cap. Thresholds, monitored volume and the way pressure or vacuum is established depend on the installed system. GM 21-NA-124 includes purge blockage in its P0455 guidance for covered gasoline vehicles: inability to establish pull-down can matter even without a large opening. Its P0442 guidance also emphasizes connections and valve sealing.
Purge command, valve movement, sealing and real vapor flow are separate observations. A click or fuel-trim shift is not a universal flow test. Ford’s covered summary distinguishes P0496/P0441_9B high-purge monitoring from its leak checks and includes engine-off natural-vacuum evaluation for P0456. Match the complete code and monitor conditions.
Inspect a cap or filler closure using the vehicle’s instructions where one is fitted. There is no universal click count or cap-first repair. Reseating does not prove sealing, and an absent warning after a few trips does not establish that the monitor completed. Save the complete scan and readiness information before clearing faults.
Have the prescribed leak, flow and input checks performed with approved EVAP equipment, medium and pressure/vacuum limits. Do not use unregulated shop air or an improvised smoke source. A leak can behave differently under pressure and vacuum; seeing no smoke does not by itself identify a bad sensor. Repair the demonstrated fault and verify the actual monitor. Strong fuel odor, leakage or severe running symptoms need prompt assessment.
Identify the circuit on your vehicle
Match the full DTC, reporting module, and any failure-type suffix to the service information for your exact year, make, model, engine, and equipment. An identifier alone does not establish installed hardware count, location, connector pinout, or a universal measurement.
Where the manufacturer publishes its own meaning for this code, that is the one to work from — it describes the actual component on your vehicle, which the generic definition cannot. Keep the generic description for what it is good for: it tells you which subject area the standard assigned the code to, which is useful context when the two appear to disagree. If they do disagree, follow the manufacturer.